1. Field of the Invention
This invention relates to the use of N-alkyl and/or N-alkenyl aspartic acids as co-collectors in the flotation of non-sulfidic ores, and to a process for the separation of non-sulfidic ores by flotation.
2. Statement of Related Art
Flotation is a separation technique commonly used in the dressing of mineral raw materials for separating valuable minerals from the gangue. Non-sulfidic minerals, such as for example apatite, fluorite, scheelite and other salt-like minerals, cassiterite and other metal oxides, such as titanium or zirconium oxides, and also certain silicates and aluminosilicates can be dressed by flotation processes. For flotation, the ore is subjected to preliminary size-reduction, dry-ground, or preferably wet-ground, and suspended in water. Collectors are normally added to these suspensions, frequently in conjunction with auxiliary reagents, such as frothers, regulators, depressors (deactivators) and/or activators in order to facilitate separation of the valuable minerals from the gangue constituents of the ore in the subsequent flotation process. These reagents are normally allowed to act on the finely ground ore for a certain time (conditioning) before air is blown into the suspension (flotation). A froth is thus produced on the surface of the suspension, the collector having a hydrophobicizing effect on the surface of the minerals. The minerals adhere to the gas bubbles formed during the aeration step, the mineral constituents being selectively hydrophobicized so that the unwanted constituents of the ore do not adhere to the gas bubbles. The mineral-containing froth is stripped off and further processed in known manner. The object of flotation is to recover the valuable mineral of the ores in as high a yield as possible while at the same time obtaining a high enrichment level.
Anionic and cationic surfactants are predominantly used as collectors in the flotation of non-sulfidic ores. These collectors are intended to be selectively adsorbed to the surface of the valuable minerals in order to obtain a high enrichment level in the flotation concentrate. In addition, the collectors are intended to form a buoyant, but not too stable flotation froth. For ores containing gangue minerals which are not hydrophobicized by anionic collectors, such as for example unsaturated and saturated fatty acids, particularly tall oil fatty acids and oleic acids, alkyl sulfates or sulfonates, it is sufficient to use anionic surfactants such as these as collectors. Ores that are more difficult to float, such as tin ores for example, require more selective collectors, such as for example phosphonic acids (German Pat. No. 2,443,460 and East German Pat. No. 76,974), or alkyl sulfosuccinamides (U.S. Pat. No. 3,830,366).
Suitable organic phosphonates for the flotation of non-sulfidic ores, particularly tin ores, include water-soluble salts or organic phosphonic acids, for example salts of styrene phosphonic acid, as described for example in the Xth International Mineral Proc. Congress--IMM, E. Topfer, pages 626 to 627, London, 1973 (O. S. Bogandow).
Collectors frequently used in the flotation of non-sulfidic ores are, for example, alkyl monocarboxylic acids, such as for example unsaturated long-chain fatty acids, such as the tall oil fatty acid disclosed above. However, di- and tricarboxylic acids are also used as collectors for flotation (H. Schubert, H. Baldauf, A. Serrano, XIIth International Mineral Proc. Congress, Sao Paulo, 1977).
By virtue of their surfactant character, many collectors for non-sulfidic ores themselves develop a froth suitable for flotation. However, it may also be necessary to develop or suitably to modify the froth by special frothers. Known flotation frothers include C.sub.4 -C.sub.10 alcohols, propylene glycols, polyethylene glycol or polypropylene glycol ethers, terpene alcohols (pine oils), and cresylic acids. If necessary, modifying reagents, for example pH regulators, activators for the mineral to be recovered in the froth or deactivators for unwanted minerals in the froth and possibly even dispersants are added to the flotation suspensions (pulps).
In many cases, the anionic and nonionic collectors used for the flotation of non-sulfidic ores do not lead to satisfactory recovery of the valuable minerals when used in economically reasonable quantities.